The broad objectives of the research in progress are to determine what role the thymus, various immunoglobulin classes and the products of the H-2 linked immune response genes play in the immune response and during tolerance induction. In particular, we are attempting to determine whether the suppressive role played by the thymus during tolerance induction is mediated via lymphokines or hormones or through production of thymus dependent antibody with resultant immune complex formation. Tolerance induction in T cells at various stages of their maturation is also being investigated with special reference to thymus dependency. The relationship between the products of the Ir genes, responsible for responsiveness to soluble protein antigens in mice and the products of other genes of the major histocompatibility locus (H-2), particularly the locus responsible for mixed lymphocyte reactivity in mice is being studied. We also hope to determine the nature of the stimulus resulting in the differentiation of lymphocytes into IgA producing plasma cells in the gut-associated lymphoid tissue.